My configuration:PIV 2.24Ghz512 Mo DDrGeForce 4 128 Mo DDRCreative AudigyWhich Windows should i use in order to run Fs 2004 with at least 20 fps and with settings set at 75%?

Either or. The OS is not really that vital to FPS, at least in my experience. I would go for XP, just because of the non-fs related benefits.

The operating system doesn't matter when it comes to framerates. It's going to be essentially the same with either. But I think you need to go with WinXP if for no other reason than future compatibility of add-ons. There are already several major add-ons that either won't work with Win98 or won't work very well. And the time is coming when the majority of the developers will stop supporting Win98 altogether. As far as whether your system can generate 20 FPS minimum at 3/4 on the sliders, the answer is "sometimes". It all depends on the specific aircraft, scenery, weather, etc. Doug

Go for XP - for all the reasons above - plus the fact that XP is much more stable than 98.Dave

An interesting and timely question. Recently, my kids computer died so I have to build them a new one. Now around our house everyone knows that means upgrade time for Dad! I thought this would also be a good time to upgrade from 98SE to XP Pro. Since I was changing mobo, processor, hard disk and OS, I decided to do the upgrade in two stages so I could see the impact, if any on FS performance. When I changed the motherboard, processor and chipset driver I saw a huge increase in FPS on 98SE but I still had a little bit of stuttering, mostly on final approach. After changing the hard disk and OS, FPS remained about the same as on 98SE but the sim was much smoother with virtually no stuttering. No, I do not run FS9 with all my sliders maxed out.:-)Someone else had posted that add-ons may not be compatible with Win98 and I can verify that is true. When I went to purchase Ultimate Traffic a while back there was a caution that it was designed for Windows XP and that it may or may not work with Win98. I gambled and bought it anyway and it appeared to work fine. Or so I thought. After installing the new hard disk and OS, I now had FS9 and Ultimate Traffic installed on two drives with two different operating systems. I was able to configure both programs identically and do some comparisons and, at least in my case, FS9 with Ultimate Traffic runs much smoother on Win XP.